From DE-Gbm 84 07 945 a spinning beam is known which is provided with a circular cross section. As an advantage of the embodiments made therein it is stated that the nozzle packages where the filaments are formed and the spinning pumps which convey polymers into these packages are enclosed by side walls and that the intermediate space is filled directly and evenly with vaporous heat carriers. A similar arrangement is shown in EP 163 248 (FIG. 4).
To prevent heat losses, the spinning beams are substantially insulated on the outer surfaces. It is not possible from a design point of view to sufficiently insulate the outer surface for facing downwards in the zone of the nozzle packages as owing to increased layer thickness the instant cooling of the filaments directly after their exit from the nozzle bores by bringing up a cooling device, in particular a blow shaft, would be prevented.
As particularly during the production of very fine filaments the quantity of the passing molten polymer is relatively small, so that heat losses either cannot be offset or are very difficult to offset again by supplying heat from the molten polymer, spinning beams must be supplied, as was outlined above, with a heat carrier heated up to the vapor phase, so that the said heat losses can be offset by the condensation of the vapor.
In this respect it is particularly important to heat the uninsulated spinnerets sufficiently and evenly. This object can only be achieved insufficiently with the spinning beams in accordance with the state of the art, because particularly in this zone the heat transfer by condensation of a vaporous heat carrier is limited most strongly owing to the unfavorable geometrical situation and the accumulating condensate and, at the same time, the heat losses of the beam are at its highest owing to the insulation which can be arranged only insufficiently.
Examples of measures that have been undertaken to this point to solve the problems of adequate heat transfer to the spinneret are disclosed in EP-A-163248. The measures mentioned above are mainly aimed at forming a heat transfer path (a "heat bridge") between the rigidly mounted carrier parts and the nozzle package. It is assumed generally (without providing any further information) that the system is capable of supplying the required heat quantity to the carrier end of the heat bridge. This assumption is not justified that easily.